A number of advanced energy storing device technologies have recently been developed, such as metal hydride (e.g., Ni--MH), lithium-ion, and lithium polymer cell technologies, which promise to provide high energy generation for a wide range of commercial and consumer applications. In high-energy applications, a substantial number of individual energy storing devices or systems are typically connected in series to produce a requisite amount of electrical power. By way of example, it is believed that a battery system suitable for powering an electric vehicle will likely have a voltage rating on the order of several hundred volts, and a current rating on the order of several hundred amperes.
In applications in which such energy storing devices are encased in an electrically conductive enclosure or housing, it is considered desirable to electrically isolate the energy storing devices from the enclosure. It is known, for example, that the development of a low resistivity current path or short between an energy storing device and a protective enclosure generally leads to the progressive degradation of the energy storing device over time.
In the case of a partial fault, a single breach or short develops in an insulation layer separating the enclosure walls from the energy storing devices. As a result, the enclosure becomes energized to a potential equal to that of a junction within the series connected energy storing devices where the breach developed. If detected at an early stage, the defect may be repaired. If left undetected, a low impedance current path may further degrade into a full short-circuit condition, and, more concerning, additional low resistivity current paths may also develop. In the case of a full fault, two or more low impedance paths between the energy storing devices and the enclosure develop due to degradation in the insulation layer. A full fault condition results in the production of a dangerous and potentially catastrophic circulating current within the enclosure.
Single and multiple internal shorts that develop between a protective housing and one or more energy storing devices encased therein are often undetectable when measuring the potential across the housing terminals or the current produced by the energy storing devices. The effect of a partial or even a full fault condition on the potential and current flow of an energy storing device or system is often minimal during the early service life of the energy storing system. If such internal faults remain undetected, however, the overall service life of the energy storing system may be significantly reduced, and unexpected and potentially violent failure of the power system may occur without warning.
There is a need in the battery manufacturing industry for an apparatus and method for effectively detecting the presence of internal short-circuit conditions arising in an encased energy storing system. There exists a further need for such an implementation which is also capable of identifying which of several series connected independent energy storing systems have been subject to an internal short-circuit condition. The present invention fulfills these and other needs.